Face films and pressure sensitive laminates for printing

ABSTRACT

Microporous structures in face films are described for improving printability of the films. Also described are laminates and pressure sensitive adhesive laminates including the microporous structured face films. Various related methods are additionally described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application and claims priority fromU.S. nonprovisional application Ser. No. 15/435,256 filed Feb. 16, 2017which claims priority from U.S. provisional application Ser. No.62/304,991 filed on Mar. 8, 2016.

FIELD

The present subject matter relates to a low cost print media for usewith a wide array of inks and printing technologies, and particularlysolvent and water based inkjet printing which requires the print mediato rapidly absorb ink liquid to provide dry print and good imagequality.

BACKGROUND

Digital inkjet printing is widely used in imaging graphics, banners,labels, etc. This printing technology attracts a wide range ofapplications due to its short turnaround time, and flexible modificationof the image used for each impression.

Based on the properties of the printing ink, a majority of inkjetprinting technologies can be classified as solvent based inkjet, waterbased inkjet, UV inkjet, and latex inkjet. For UV inkjet printing, a UVinkjet printer must be used which emits a UV beam to solidify theprinted ink. Latex inkjet printers are equipped with one or more highcapacity heater(s) to evaporate water in the printed ink in a relativelyshort time. Solvent inkjet printers, especially those using high boilingpoint solvent in the ink, and water inkjet printers typically do nothave enough heating capacity to remove the residual liquid in theprinted ink. Instead, those printers require print media able to absorbmost of the liquid ejected from the print head in a relatively shorttime to control the formation of ink dots on the media and attain a “dryto touch” characteristic after printing. For example, Eco-Sol Max inkused in Roland Eco-Sol inkjet printers contains over 90% of a mixture ofdiethylene glycol diethyl ether (boiling point=189° C.), r-butyrolactone(boiling point=204° C.), and tetraethylene glycol dimethyl ether(boiling point=275° C.). The printer heating bed is typically heated upto 50° C. Dye or pigment water based inkjet ink used in desktop ornarrow web printers typically contains 90% water and the printersequipped with these inks generally have no media heating capability.

Most ink receptive layers used in currently available print mediadesigned for solvent inkjet printers use solvent swellable polymers andabsorptive filler to “lock in” the liquid in the media during print. Theselection of the polymers is based on solubility parameters betweenpolymer and solvent. The solubility parameter between polymer andsolvent should be such that the polymer can swell with solvent. Typicalpolymers used in conventional ink receptive layers include vinyl,acrylics, polyacrylate, polyurethane, amorphous polyester, polyether,polyvinyl alcohol, etc. In order to provide enough absorption capacity,the ink receptive layer has to be thick enough, typically at least 25microns, to absorb the volume of liquid ink deposited on the printmedia. This makes the resulting media material relatively costly.

Polyolefins are much less expensive than the swellable polymericmaterials previously noted. The average cost of polyethylene andpolypropylene is approximately 25% of the cost of polymers such aspolyurethane, polyvinyl alcohol, amorphous polyester, etc. However,solid polyolefin films such as polyethylene and polypropylene have noaffinity to most polar solvents used in solvent inkjet printing andwater used in water inkjet printing in the market. As result, films witha layer or coating of polyolefin(s) as an ink receptive surface do notsufficiently absorb the ink liquid and thus the media is relatively wetafter print and exhibits poor printing image quality, namely low imageresolution and ink bleeding. As will be appreciated, this isundesirable.

Accordingly, a need remains for strategies by which polyolefin films andother materials which do not have a sufficient affinity for polarsolvents used in solvent inkjet printing and/or water used in waterinkjet printing, can be used as print media. A need also exists for anew class of print media which addresses the above noted problems.

SUMMARY

The difficulties and drawbacks associated with previous approaches areaddressed in the present subject matter as follows.

In one aspect, the present subject matter provides a polymeric filmadapted for absorbing liquid inks from inkjet printing. The film definesa first face for receiving print, and a second oppositely directed face.The film includes a microporous structure extending along at least thefirst face. The microporous structure has a porosity within a range from40% to 75%. The microporous structure includes a plurality ofinterconnected pores having a pore size distribution within a range offrom 2 microns to 10 nm. The microporous structure has a thickness of atleast 20 microns as measured from the first face. The film exhibits anink absorption rate of at least 0.01 picoliter/μm²/second at a printingtemperature of 40° C.

In another aspect, the present subject matter provides a laminatecomprising a polymeric film adapted for absorbing liquid inks frominkjet printing. The film defines a first face for receiving print, anda second oppositely directed face. The film includes a microporousstructure extending along at least the first face. The microporousstructure has a porosity within a range from 40% to 75%. The microporousstructure includes a plurality of interconnected pores having a poresize distribution within a range of from 2 microns to 10 nm. Themicroporous structure has a thickness of at least 20 microns as measuredfrom the first face. The film exhibits an ink absorption rate of atleast 0.01 picoliter/μm²/second at a printing temperature of 40° C. Thelaminate also comprises at least one core layer disposed along thesecond face of the film.

In yet another aspect, the present subject matter provides an adhesivelaminate comprising a polymeric film adapted for absorbing liquid inksfrom inkjet printing. The film defines a first face for receiving print,and a second oppositely directed face. The film includes a microporousstructure extending along at least the first face. The microporousstructure has a porosity within a range from 40% to 75%. The microporousstructure includes a plurality of interconnected pores having a poresize distribution within a range of from 2 microns to 10 nm. Themicroporous structure has a thickness of at least 20 microns as measuredfrom the first face. The film exhibits an ink absorption rate of atleast 0.01 picoliter/μm²/second at a printing temperature of 40° C. Theadhesive laminate also comprises a layer of adhesive disposed along thesecond face of the film.

In still another aspect, the present subject matter provides a method offorming a polymeric film adapted for absorbing liquid inks from inkjetprinting. The film includes a microporous structure extending along atleast one face of the film. The method comprises extruding polymer toform a film. The method also comprises stretching the film to a stretchratio within a range of from 1:1.1 to 1:10 such that the microporousstructure has a porosity within a range from 40% to 75% and includes aplurality of interconnected pores having a pore size distribution withina range of from 2 microns to 10 nm.

As will be realized, the subject matter described herein is capable ofother and different embodiments and its several details are capable ofmodifications in various respects, all without departing from theclaimed subject matter. Accordingly, the drawings and description are tobe regarded as illustrative and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section of an embodiment of a pressuresensitive adhesive laminate in accordance with the present subjectmatter.

FIG. 2 is a schematic cross section of an embodiment of a face filmhaving an absorption layer or region(s) in accordance with the presentsubject matter.

FIG. 3 is a schematic cross section of an embodiment of a multilayerface film having an absorption layer or region(s) in accordance with thepresent subject matter.

FIG. 4 is a graph showing extent and rate of ink absorption as afunction of time of several print media samples in accordance with thepresent subject matter compared to conventional print media.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Generally, the present subject matter provides films with particularmicroporous structures that provide a print receptive face useful fordigital inkjet printing and especially solvent inkjet printing and/orwater inkjet printing. In many embodiments, the films are adapted forabsorbing liquid inks in inkjet printing which requires the film toabsorb the liquid component in the ink to thereby dry the ink andprovide good print quality. The microporous structures can be formed orotherwise incorporated in a wide range of films and other substrates toprovide a print receptive face. The microporous structures areparticularly useful for incorporation in polyolefin films such aspolyethylene films and polypropylene films to provide a printable mediawith low cost.

In many embodiments, the present subject matter provides low costpressure sensitive (PSA) laminates with an open cell microporousstructured liquid absorptive layer constituting a print receptive facethat exhibits good ink fluid management characteristics, good printimage quality and fast drying speeds to enable the laminates to be usedin digital inkjet printing, and especially absorption based inkjetprinting technology using high boiling point solvent inkjet printing andwater based inkjet printing. For these types of printers, usually theprinters do not have enough heating capability to evaporate the inkliquid after printing. Instead, these printers primarily rely on a printreceptive face of the print media to absorb the ink liquid into theunderlying media in a relatively short time. The laminates are alsoprintable with other non-absorption based inkjet printing such as latexinkjet printing and UV inkjet printing. The laminates are also printablewith other non-inkjet printing technologies such as toner laserprinting, flexographic printing, gravure printing, screen printing, etc.

Referring to FIG. 1 , in many embodiments, the PSA laminates 10 comprisea top film 20, a layer 30 of pressure sensitive adhesive disposed in amiddle or interior region, and a release liner 40 removably covering theadhesive layer 30 on the back. The film on the top is referred to hereinas a “face film” and this film can be in the form of a single layerextruded film, a multilayer extruded film, a coated film, and/or alaminated film.

Referring to FIG. 2 , the face film 20 defines a print receptive face22, an opposite face 24, and includes an absorption layer 26 orregion(s) resulting from a microporous structure. The absorption layerextends immediately alongside the print receptive face 22 of the facefilm 20 and the laminate 10. For a single layer face film such as shownin FIG. 2 , the face film 20 comprises an open cell microporousstructure within region 26 that has open cell interconnected poresforming continuous channels for ink fluid absorption.

FIG. 3 illustrates a multilayer face film 50 comprising an outer layer60 defining a print receptive face 62, an opposite face 64, and anabsorption layer 66 or region(s) resulting from a microporous structure.The absorption layer 66 extends immediately alongside the printreceptive face 62 of the face film 50. The print receptive face 62 ofthe face film 50 comprises an open cell microporous structure. Themultilayer face film 50 also comprises one or more additional layerssuch as layers 70, 80 disposed along the face 64 of the outer layer 60.Each of the layers of the multilayer face film can differ in chemicalcomposition or be the same or substantially the same. The multilayerface film 50 can be in the form of multiple extruded layers. For alaminated face film, the print receptive face comprises an open cellmicroporous structure and the layers under the print receptive face canbe either a solid film layer or a porous film. The various layers aretypically bonded together by adhesive, heat, or other chemicals. One ormore tie layers can be used. In particular embodiments, the multilayerface film includes a plurality of layers in which a first layer extendsalong the print receptive face, and a second layer extends along anoppositely directed face of the film. One or more additional layers canbe disposed between the first and second layers. The microporousstructure can extend (i) partially through the first layer, (ii)entirely through the first layer, (iii) entirely through the first layerand partially through the second layer, or (iv) entirely through boththe first and second layers.

A majority of liquid absorption properties of the top layer or region(s)along the print side result from a liquid capillary flow effect of theopen cell microporous structure. The thickness of the microporousstructure layer on the print receptive face is at least 20 microns toprovide sufficient liquid absorption capability. Referring to FIG. 2 forexample, this means that the thickness of the absorption layer 26 of theface film 20 is at least 20 microns. The microporous structure of theabsorption layer can extend the entire thickness of the face film, or asshown in FIG. 2 , extend for only a portion of the thickness of the facefilm.

The porosity of the microporous structure layer or region is at least40%, i.e., 40% by volume void content, to provide a relatively fastliquid absorption speed which thereby enables fast ink drying andaccelerated printing speed. The porosity of the microporous structurelayer or region is at least 40%, and may range from 40% up to about 75%depending upon particular applications. In certain embodiments, theporosity is within a range of from 40% to 70%, and in particularembodiments, the porosity is within a range of from 40% to 60%. Thereare several different methods to characterize the porosity of film. Theporosity measured in the description herein of the present subjectmatter is determined by the bulk volume method.

The pores accessible along the print receptive face and/or inside themicroporous region are open cell and interconnected to form continuousor substantially continuous channeling for liquid flow, typically viacapillary flow. The pore size distribution is in the range of from about2 microns to about 10 nanometers. In a microporous structure, internalvoids, pores, or cells can be characterized as either closed cell oropen cell based upon their wall. The term “closed cell” as used hereinrefers to cells in which the wall of an individual cell is continuousand without openings so that the cell is sealed, and thus there are nochannels or apertures between the cells to allow liquid flowtherethrough. The term “open cell” refers to cells that aredistinguishable from closed cells in that the wall of an individual opencell includes one or more openings which can form interconnectedchannel(s) or aperture(s) to allow liquid flow therethrough. The term“open cell microporous structure” refers to a microporous structurecomprising open cells and interconnected channels. In many embodiments,the open cell microporous structure comprises a majority, i.e., greaterthan 50%, of open cells and a minority, i.e., less than 50%, of closedcells. In many embodiments, the open cell microporous structure extendsfrom one side of a porous film surface to another side of the porousfilm surface. The rate or speed of liquid absorption of the open cellmicroporous structure generally depends on the pore size, amount of theopen cells, porosity, and surface tension. In label technology, certainfilms are referred to as “cavitated films”. The main differences betweencavitated films and many of the film embodiments of the present subjectmatter that include open cell microporous structures are (1) that amajority of the cells in cavitated films are not open cells and they arenot interconnected, and (2) cavitated films typically exhibit a sealedsurface or face, i.e., no pores or openings on the surface or face.

In some embodiments, the ink absorption rate of the microporous film attypical printing conditions is at least 0.01 picoliter/μm²/second tothereby provide quick drying of print. In additional embodiments, theink absorption rate is at least 0.05 picoliter/μm²/second, moreparticularly at least 0.10 picoliter/μm²/second, more particularly atleast 1.0 picoliter/μm²/second, more particularly at least 10picoliter/μm²/second, more particularly at least 100picoliter/μm²/second, more particularly at least 1,000picoliter/μm²/second, more particularly at least 10,000picoliter/μm²/second, and more particularly at least 100,000picoliter/μm²/second. These ink absorption rates are at a printingtemperature of 40° C.

In some embodiments, a microporous film is provided having relativelysmall pores along its face. For example, a film having pores with amaximum opening dimension or span of 1 micron or less can be used toincrease surface gloss, promote surface appearance, and/or increaseprint ink color intensity. Although not wishing to be limited to anyparticular theory, it is believed that the use of such small pores alonga film face reduces the potential of pigment particles being depositedwithin the pores or otherwise not residing along the film face.

In particular embodiments, the open cell microporous layer whichconstitutes or includes the absorption layer of the top or face filmcomprises polymer, air voids, and optional additives and/or agents suchas inorganic filler. In many embodiments, the face film comprises atleast 30% polyolefins, and in particular embodiments at least 40%polyolefins. In certain embodiments, approximately 50% by weight ofpolymer in that layer or region is polyolefin or modified polyolefinsuch as polypropylene, polyethylene, polypropylene copolymer,polyethylene copolymer or the like. Combinations of polymeric materialscan be used. One or more particulate agents can be included. A typicalsize for the particulate agent is in the range of several microns orless. The additives may include one or more of a nucleating agent, ananti-blocking agent, a processing aid, a slip agent, an antistaticagent, a pigment, a cavitating agent, an inorganic filler, a heatstabilizer, an antioxidant, a flame retardant, an acid acceptor, avisible and/or ultraviolet light stabilizer, a surfactant, or a mixtureof two or more of any of the foregoing additives. The additives can bepresent in the above described polymers or films as supplied by a vendoror can be introduced into the film or a film layer as an additiveconcentrate where the additive is present generally from 1% to 75%, moreparticularly from 30% to 70%, and in particular embodiments from 40% to65% by weight, depending on its use. Additives for use in the film or afilm layer are further described in U.S. Pat. No. 6,821,592 to Rodickand U.S. Pat. No. 7,217,463 to Henderson. Nonlimiting examples ofinorganic fillers include but are not limited to calcium carbonate,silica, alumina oxide, titanium dioxide, etc.

In some embodiments, the open cell microporous structure whichconstitutes or includes the absorption layer of the top or face filmcomprises other polymers besides polyolefin. In the event such polymersare not compatible with polyolefin, separated small phase domain(s) inthe film may form prior to film stretching. This creates additionalsmall sized pores after film stretching. Nonlimiting examples of otherpolymers include polystyrene, styrene copolymers, polyurethane,polyester, polyacryl or polymethacryl resin, polycarbonates, ionomers,and combinations thereof.

The open cell microporous structures can be formed by stretching amultiphase separated polymer film or sheet(s) in a machine direction(MD) or both machine and cross directions (CD). A wide range of stretchratios can be used to form embodiments of the face films of the presentsubject matter. Typically, a stretch ratio greater than 1:1 can be used,and in particular embodiments, the stretch ratio is greater than 1:4.The upper limit or maximum stretch ratio depends upon the applicationand film material(s), however, a maximum stretch ratio of about 1:10 iscontemplated. Thus, a range of stretch ratios according to this aspectof the present subject matter is from 1:1.1 to 1:10. In manyembodiments, a stretch ratio within a range of from 1:2 to 1:8 can beused and more particularly from 1:4 to 1:6. Stretching the film can beperformed inline or offline. As noted, stretching can be performed in asingle direction or in multiple directions. The stretching ratiorequired to obtain at least 40% porosity and fast enough absorptionspeed for solvent inkjet printing varies with the material chemicalcomposition, phase morphology and stretching temperatures. But in manyembodiments, the existence of multiple phase domains and the pooradhesion between different phase domains in the film prior to thestretching is essential to creating a microporous structure afterstretching. For example, a microporous film can be formed by stretchingfilms containing beta polypropylene crystal phase or films containingCaCO₃ and/or one or more other inorganic fillers. An example ofpolypropylene beta nuclear agent is MPM2000 from Mayzo, Inc. Additionaldetails of forming microporous structures are provided herein. Methodsand techniques for stretching films and stretching to particular stretchratios are known in the art and thus not described herein. For example,descriptions of such aspects are provided in one or more of U.S. Pat.Nos. 6,835,462; 5,709,937; 7,217,463; 7,410,706; 6,376,058; 6,663,947;and 5,585,193.

In certain embodiments, the method to produce a microporous filmincludes using solvent extraction technology to selectively dissolve onecomponent of the film and remove that component and thereby create aporous structure. The solvent extraction step can be performed before orafter film stretching or without film stretching. The solvent used inthis embodiment is selected so as to be able to dissolve at least onecomponent in the film and not dissolve other components. After removalof the one or more component(s) in the film, the film is dried and thelocation of the removed component constitutes the pores.

In certain embodiments, a thin coating may be applied on the face filmand particularly upon the print receptive face, to enhance the ink dyeor pigment spreading or anchorage and/or other aesthetic properties suchas surface gloss. The coating thickness is typically less than 15microns. In many embodiments, the coating is disposed on one or both ofthe faces of the film. In certain embodiments, the coating includes amicroporous structure and particularly an open cell microporousstructure. In certain embodiments, the coating includes one or moresurfactants which increase the surface energy of the coating to therebyincrease liquid absorption.

The present subject matter also provides laminates which include thenoted face film(s). In certain embodiments, the laminates may includeadditional layers under the top or face film. The layers under the oneor more top film(s) are referred to herein as “core layer(s)”. The corelayer(s) can be either a solid, i.e., nonporous, film or a porous filmwith the same or different porous structure as the absorption layer ofthe face film. That is, in particular embodiments, the one or more corelayer(s) include a microporous structure that has a porosity within arange of from 40% to 75%, and/or includes a plurality of interconnectedpores having a pore size distribution within a range of from 2 micronsto 10 nm. The core layer(s) may, in certain embodiments, provide themechanical or other properties for the laminate. By using soft or stiffpolymer(s) in the core layer, a soft or stiff face film can be achieved.For example, a soft print laminate can be made with linear low densitypolyethylene (LLDPE) in the core layer and a rigid print laminate can bemade with polypropylene (PP) in the core layer.

In many applications, a user images the print side of a laminate, suchas the laminate 10 of FIG. 1 , then removes the liner 40 to expose thepressure sensitive adhesive 30 to a substrate of interest. Pressuresensitive adhesive anchors the imaged film on targeted substrates.

In many embodiments of the present subject matter, the print layer ofthe pressure sensitive laminate typically includes a polyolefin basedopen cell microporous liquid absorptive layer on a major print surface.The polyolefin molecule itself does not absorb the polar ink solvent.The capillary flow effect created by the high porosity structureprovides the driving force for liquid absorption of both polar andnon-polar solvent(s). Since the absorption is from a capillary floweffect, the microporous absorptive layer can absorb the inkjet inkliquid regardless of the chemical type, such as from non-polar solventsto highly polar solvents. The layer or layers underneath the absorptivelayer provide mechanical or other properties for the laminate material.Also, by utilizing a high porosity structure, the solvent absorptionspeed of the absorption layer can be significantly faster thanconventional absorptive swellable polymer(s), typically by an order ofmagnitude, thereby improving printing efficiency.

Additional details and aspects of the present subject matter are asfollows.

Adhesives

As noted, in many embodiments, the laminates may utilize one or morelayer(s) or region(s) of adhesive. For example, as shown in FIG. 1 , thelaminate 10 includes a layer 30 of pressure sensitive adhesive.

The adhesive layer may comprise a pressure sensitive adhesive (PSA)which bonds the laminate or at least portions thereof to a surface,typically under applied pressure, at room temperature. The adhesivelayer ray be a continuous or discontinuous layer, and it may compriseone or a mixture of two or more adhesives. The adhesive layer may be apatterned adhesive layer with relatively strong adhesive tack level insome areas and a relatively weak adhesive in other areas. In certainembodiments of the present subject matter, the adhesives are printable.

In one embodiment of the present subject matter described herein, thepressure sensitive adhesive comprises an acrylic adhesive material,particularly a crosslinked acrylic resinous material, and moreparticularly, a crosslinked acrylic emulsion. A particularly usefuladhesive material comprises an internally crosslinked acrylic emulsion.These pressure sensitive adhesive materials provide a useful combinationof low tack, peel and flow properties with a sufficient level ofcohesive strength at a relatively thin coat weight. High molecularweight acrylic adhesives and externally crosslinked acrylic adhesivesalso may be used.

The adhesive may comprise a rubber based adhesive, acrylic adhesive,vinyl ether adhesive, silicone adhesive, or mixture of two or morethereof. The adhesive may be applied to the laminate as a hot melt,solvent-based or water based adhesive. The adhesive materials that areuseful may contain as a major constituent an adhesive polymer such as anacrylic-type polymer; block copolymer; natural, reclaimed, orstyrene-butadiene rubber; tackified natural or synthetic rubber; acopolymer of ethylene and vinyl acetate; an ethylene-vinyl-acrylicterpolymer; polyisobutylene; or poly (vinyl ether). Other materials maybe included in the adhesive such as tackifying resins, plasticizers,antioxidants, fillers, and waxes.

In certain embodiments, water-based pressure sensitive adhesives can beused. And in particular embodiments, water-based pressure sensitiveadhesives are used in combination with water-based flexographic inks.

A description of useful pressure sensitive adhesives may be found inEncyclopedia of Polymer Science and Engineering. Vol. 13,Wiley-Interscience Publishers (New York, 1988). Additional descriptionof useful pressure sensitive adhesives may be found in Encyclopedia ofPolymer Science and Technology, Vol. 1, Interscience Publishers (NewYork, 1964).

Pressure sensitive adhesives that may be used include the hot meltpressure sensitive adhesives available from H. B. Fuller Company, St.Paul, Minn. Other useful pressure sensitive adhesives include thoseavailable from Century Adhesives Corporation, Columbus, Ohio.

Conventional PSAs, including silicone-based PSAs, rubber-based PSAs, andacrylic-based PSAs are useful in certain applications or embodiments.Another commercial example of a hot melt adhesive is, sold by AtoFindley, Inc., of Wauwatusa, Wis. In addition, rubber-based blockcopolymer PSAs described in U.S. Pat. No. 3,239,478 also can be used.

The adhesive compositions may contain at least one solid tackifier resincomponent. A solid tackifier is defined herein as one having a softeningpoint above 80° C. When the solid tackifier resin component is present,the adhesive compositions may comprise from about 40% to about 80% byweight of a thermoplastic elastomer component, in one embodiment fromabout 20% to about 60% by weight, and in another embodiment from about55% to about 65% by weight of a solid tackifier resin component. Thesolid tackifier reduces the modulus of the mixture sufficiently to buildtack or adhesion. Also, solid tackifiers, particularly the highermolecular weight solid tackifiers (e.g., Mw greater than about 2000) andthose having a lower dispersity (Mw/Mn being less than about 3) may beless sensitive to migration into the polymer film layer. This isdesirable since migration of tackifier into the film layer may causedimensional instability.

The solid tackifier resins include hydrocarbon resins, rosin,hydrogenated rosin, rosin esters, polyterpene resins, and other resinswhich exhibit a proper balance of properties. A variety of useful solidtackifier resins are available commercially such as terpene resins whichare sold under the trademark Zonatac by Arizona Chemical Company,petroleum hydrocarbons resins such as the resins sold under thetrademark Escorez by Exxon Chemical Company, or Wingtack 95, a synthetictackifier resin available from Goodyear, Akron, Ohio.

The adhesive layer also may contain one or more pigments to enhance theopacity of the ink layers and permit use of thinner ink layers toachieve desired levels of opacity. Examples of pigments include titaniumdioxide and carbon black. The pigment volume concentration may range upto about 10%, in one embodiment from about 5% to about 10%, and inanother embodiment from about 2% to about 8%.

The adhesive compositions also may include other materials such asantioxidants, heat and light stabilizers, ultraviolet light absorbers,fillers, colorants, antiblocking agents, reinforcing agents, andprocessing aids.

The adhesive compositions may contain inorganic fillers and otherorganic and inorganic additives to provide desired properties. Examplesof useful fillers include calcium carbonate, titanium dioxide, metalparticles, and fibers.

In certain embodiments, particular coatweights of adhesive are useful.In one embodiment, the amount of adhesive applied to the multilayerlaminate is within a range of from about 4 to 20 g/m²(gsm), andparticularly from about 6 to 15 g/m².

In particular embodiments, the adhesive is radiation curable,

Release Liners

As noted, in many embodiments, the laminates may utilize a release lineror layer having release material thereon, in contact with and generallycovering the adhesive layer. For example, the laminate 10 depicted inFIG. 1 includes a release liner 40. The release liner may be in the formof a collection of liner segments or components. The release liner istypically paper, filmic materials, or combinations thereof.

A wide variety of release materials such as those typically used forpressure sensitive tapes and labels are known, including silicones,alkyds, stearyl derivatives of vinyl polymers (such as polyvinyl stearylcarbamate), stearate chromic chloride, stearamides and the like.Fluorocarbon polymer coated release liners are also known but arerelatively expensive. For most pressure sensitive adhesive applications,silicones are by far the most frequently used materials. Siliconerelease coatings have easy release at both high and low peel rates,making them suitable for a variety of production methods andapplications. In certain embodiments, the release layer includes one ormore silicone materials.

Known silicone release coating systems generally include a reactive,silicone polymer, e.g., an organopolysiloxane (often referred to as a“polysiloxane,” or simply, “siloxane”); a crosslinker; and a catalyst.After being applied to the adjacent layer or other substrate, thecoating generally must be cured to crosslink the silicone polymerchains, either thermally or radiatively (by, e.g., ultraviolet orelectron beam irradiation).

Based on the manner in which they are applied, three basic types ofsilicone release coatings used in the pressure sensitive adhesiveindustry are known: solvent borne, water borne emulsions, and solventfree coatings. Each type has advantages and disadvantages. Solvent bornesilicone release coatings have been used extensively but, because theyemploy a hydrocarbon solvent, their use in recent years has tapered offdue to increasingly strict air pollution regulations, high energyrequirements, and high cost. Indeed, the energy requirements of solventrecovery or incineration generally exceed that of the coating operationitself.

Water borne silicone emulsion release systems are as well known assolvent systems, and have been used on a variety of pressure sensitive,products, including tapes, floor tiles, and vinyl wall coverings. Theftuse has been limited, however, by problems associated with applying themto paper substrates. Water swells paper fibers, destroying thedimensional stability of the release liner backing and causing sheetcurling and subsequent processing difficulties.

Solventless or solvent-free silicone release coatings have grown inrecent years and now represent a major segment of the silicone releasecoating market. Like other silicone coatings, they must be cured afterbeing applied to the flexible liner substrate. Curing produces acrosslinked film that resists penetration by the pressure sensitiveadhesive.

Informative descriptions of various release materials, theircharacteristics, and incorporation in laminate assemblies are providedin U.S. Pat. Nos. 5,728,469; 6,486,267; and US Published PatentApplication 2005/0074549, owned by the assignee of the presentapplication. It is also contemplated that various waxes known in the artcould be used for the release material or utilized in the release layer.

In certain embodiments of the present subject matter, the multilayerlaminates utilize release layers that are relatively thin. For example,a typical release layer thickness is from about 1 to about 4 microns. Inparticular embodiments, the thickness of the release layer is from about1 to about 2 microns.

Materials suitable for use as a release coating may include acrylics,silicones, polyurethanes, and the like. For certain embodiments, acommercially available, PET23 release liner from Mitsubishi can be used.The noted PET23 release liner is a film of polyethylene terephthalate(PET) coated with a siliconized release agent. In certain embodiments, asilicone coated paper support layer available from Avery Graphics underthe designation Sample 546 Silver can be used. That material is a whitemando backing coated with 9630 silicones at a coat weight of 1.15 g/m².Particular and additional examples of materials for use in the releasecoating may also include HYCAR 26706 acrylic emulsion available fromLubrizol Corporation, Wickliffe, Ohio, and the silicone emulsion system3200 from Dow Corning Corporation, Midland, Mich. (base silicone 5M3200,CRA agent 5M3030 and catalyst emulsion SM 3010). It may be desirable tocrosslink the polymer in the release coating to achieve an elevatedsoftening point. Certain crosslinkers that can bind reactively with thecarboxylic group of acrylic and urethane emulsions may be used. Anexample of an effective crosslinker is XAMA 7, a polyaziridine oligomerfrom Ichemco; Srl (Cuggiono, Italy). Other crosslinkers that may be usedinclude water-dispersible polyisocyanates; such as BAYHYDUR 302 and 303from Bayer Corp., and titanium and zirconium crosslinkers from E.I. duPont de Nemours and Company (Wilmington, Del.), such as TYZOR TE and LA(Ti-derived water-stable) and TYZOR ZEC (Zr-derived).

The release coating may further include additives, such as releasemodifiers, rheology agents, surfactants, leveling agents, and defoamers.Examples of such additives may include release modifiers, such as MICHEM43040 (polypropylene wax emulsion) from Michelman, Inc, (Cincinnati,Ohio), and Fluids 190 and 193 from Dow Corning Corporation (Midland,Michigan); low foam surfactants, such as TRITON CF-10 from The DowChemical Company (Midland, Mich.) and ZONYL FSO from E.I. du Pont deNemours and Company (Wilmington, Del.); rehology modifiers, such asCELLOSIZE ER15 from The Dow Chemical Company; defoamers; such as BY K 19and 24 from Byk-Chemie GmbH (Wesel, Germany): dispersing agents forinorganic fillers, such as SOLSPERSE 40000 from Lubrizol Corporation(Wickliffe, Ohio) and DISPERBYK 191, 192 from Byk-Chernie GmbH (Wesel,Germany). It is also contemplated that additional polymers such as anSBR latex could be included in the release formulation to increase therelease force, i.e., the adhesive force.

Other additives that may be included in the release coating compriseinorganic fillers, such as talc, calcium carbonate, clay, silica, etc.The presence of such inorganic fillers may give a matte-look to thefinal multilayer laminate; as well as improve the break-edge selectivityof the transferred image. Examples of such inorganic fillers may includeNYTAL 7700 talc pigment (The Cary Company, Addison, Ill.), VAI TALC PCand 4000 talc powders (R.T. Vanderbilt Company, Inc., Norwalk, Conn.),and ULTRAWHITE 90 clay (Engelhard Corporation; Iselin, N.J.). Theparticle size for the filler may be in the range of about 0.5 to 30microns, particularly about 1 to 20 microns, more particularly about 2to 10 microns.

The present subject matter can be used for graphic decoration, signage,banners, wall paper, car wrapping materials, and label applicationswhich require imaging the material with absorption based inkjetprinters, especially high boiling point solvent or water based inkjetprinters and adhering the printed film on substrates with PSA.

EXAMPLES

Various samples of printable laminates in accordance with the presentsubject matter were prepared and evaluated. The results of theevaluations are as follows.

Print Test Method

Samples were evaluated for printability using both a wide format highboiling point polar solvent type inkjet printer and a desktop waterbased inkjet printer.

In evaluating media printability with the polar solvent based inkjetprinter, printing was conducted on a face film with a wide formatEco-Solvent inkjet printer Roland Soljet Pro II XC-540 printer(available from Roland Company) equipped with Eco-Sol Max inkjet inks.An image file with graphics and color bleeding pattern was printed onthe face film with AVERY MPI1005SC ICC profile to check the imagequality and resolution. The temperature control of the printer was setas: preheat 40° C./printer heat 40° C./drier heat 50° C. Dryness of theprint was evaluated by applying a piece of copy paper over the top ofthe print with a pressure roller when print was immediately exiting theheating bed of the printer. The copy paper was removed to assess whetherthere was wet ink transferred to the paper. No noticeable ink transferwas considered “dry to touch.” An image file with a set of solid colorblocks with 25%, 50%, 75%, 100% ink load of cyan, magenta, yellow andblack ink respectively, were printed on films with the ICC profileturned off to determine the ink density of the media. The ink densitywas measured by an X-Rite eXact™ spectrophotometer.

In evaluating media printability with the water based inkjet printer,various film samples were selected to print with an Epson WF-3520desktop water based inkjet printer. Dryness of the print was evaluatedby applying a piece of copy paper over the top of the print with apressure roller as the print sheet ejected out from the printer. Thecopy paper was removed to see whether wet ink transferred to the paper.No noticeable ink transfer was considered “dry to touch.” The printerwas not equipped with any media drying heater(s).

Ink Absorption Properties Evaluation

The ink absorption properties of the samples were evaluated by twomethods: (i) IGT ink penetration test by using an IGT Printabilitytester type A1 and (ii) ink absorption and spreading test by use of anautomatic microscopic contact angle meter MCA-3 from KYOWA InterfaceScience Co. Ltd. In the IGT ink penetration test, a drop of ink waspassed through a nip utilizing a known, controlled pressure. One side ofthe nip held a sample of the material being tested. As the ink dropletpassed through the pressurized nip, the ink spread out, creating a stainon the test material. The length of the stain was measured to determinethe material's holdout properties. In the ink absorption and spreadingtest, a picoliter drop of Eco-Sol max black ink was ejected from aninkjet nozzle on a sample surface. A high speed optical microscopecamera captured unabsorbed ink drop absorption and spreading images asfunctions of time. Then ink drop contact angle, diameter, as well asvolume left on the sample surface as functions of time were calculatedby imaging processing software.

Face Film Preparation Process

Certain face film samples listed in the examples were prepared by usinga multilayer conventional co-extrusion film cast line equipped with fourextruders A, B, C, D and up to a 7 layer feed block and a set of inlinemachine direction orientation (MDO) stretching units manufactured byLabTech Engineering company Ltd. Each extruder supplied a meltformulation to a symmetric feedblock (feed block structure ABCDCBA)where the melts were combined to form a single molten stream consistingof a multilayer formulation. The molten stream was cast onto a castroll, solidified, and moved to an in-line MDO section. In the MDOsection, the film sheet was reheated and stretched at a certain drawdown ratio and then annealed in the annealing rolls, then cooled andwound into a film roll in the end. The resin formulation in extruder A,B, C, D could be the same or different based on the film layerstructure. For example, a single layer film was made by feeding allextruders A, B, C, D, the same resin formulation and a two layer filmwas made by feeding extruder A the same resin formulation as B andfeeding extruder C the same resin as D. A valve in the feedblock foreach layer was provided which could be turned off so a non-symmetricfilm structure could be made. The layer thickness ratio of themultilayer film was controlled via the ratios of each extruder. Biaxialstretched samples were prepared as follows. A thick cast sheet wasformed using an extrusion line without going through the MDO stretchingunit. Then, the cast sheet was stretched using biaxial orientation in aKaro IV Laboratory Stretcher offline (manufactured by BrucknerMaschinenbau GmbH, Siegsdorf, Germany). The extrusion, MDO and biaxialtemperature conditions were adjusted based on material formulation toprovide uniform samples. All the film samples had a thickness of atleast 25 microns thick, if not otherwise specified.

Example A

A single layer porous polyethylene (PE) film with different stretchratios was prepared as follows. Mix 75% CaCO₃/LDPE master batch resinpellet (Colortech 40002-08, master batch with 75% CaCO₃ and 25% LDPE,density=1.82) and 25% LLDPE resin pellet (Dowlex 2056G; MI=1.0;density=0.92). Total proportions in the blend resin were 56% CaCO₃ and44% PE. Feed resin pellet blend in extruder A, B, C and D. The extrudertemperature was set as 420° F. Cast roll and MDO rolls temperatures wasset as two cast roll T=120° F.; pre-heat 1, 2, 3, 4, 5 rolls T=195° F.;stretching 1, 2 rolls T=185° F.; annealing 1 and 2 rolls T=195° F.; andcooling roll T=70° F. To produce film samples with different stretchingratios, the draw ratio between stretching roll 1 and stretching roll 2was set at 1:1, 1:2, 1:3, 1:3, 1:3.5, 1:4.5, 1:5 respectively for eachsample. Corresponding samples collected were labeled as samples A-1X,A-2X, A-3X, A-3.5x, A-4.5X, and A-5X. The printing results of samplesare listed below. The porosity of the samples was calculated based ondensity.

Table 1 lists the Eco-Sol inkjet printer printing result of example Asamples. Compare-1, and -2 samples are two commercial wide format inkjetprintable non-microporous film products manufactured by AVERY DENNISON.Compare-3 sample is a solid PE film. Due to the non-polarity of PE andhigh polarity of the ink solvent, solid PE film has very low inkabsorption. As a result, print was very wet and ink drops on the printsurface flew into each other and led to very poor image resolution.Sample A-1X included 56% slightly porous CaCO₃ filler within the PE, butno machine direction stretching. This sample printed slightly betterthan the Compare-3 sample due to the CaCO₃ filler. However, this sampleexhibited very wet properties and poor image quality. From sample A-1Xto A-5X, as the stretching ratio increased, more interconnected poreswere created. When a ratio of 3 times stretching was reached, theporosity created provided enough absorption capability for print, so theprint reached a “dry to touch” characteristic.

TABLE 1 Eco-Sol Inkjet Printer Printing Result of Example A andReference Samples Sample ID Sample Description Print Dryness PrintQuality Compare-1 AVERY MPI ™ 1005 Dry, no ink Good cast vinyl filmtransfer resolution Compare-2 AVERY TMP ™ 7000 Dry, no ink Goodnon-vinyl film with transfer resolution polyurethane print skinCompare-3 50 micron single Very wet, over Nearly no layers LDPE film 80%ink trans- resolution. made from 100% ferred to paper Dowlex 2056G. nostretching in MD A-1X stretching ratio 1:1 Very wet, Nearly noapproximately resolution. 50% ink trans- ferred to paper A-2X stretchingratio 1:2 Slightly wet Poor at dark color, resolution. approximatelyBetter than 30% ink trans- A-1 ferred to paper A-3X stretching ratio 1:3Dry to touch Good image resolution, ink color density is slightly lowercompared with Compare-1 A-3.5X stretching ratio 1:3.5 Dry to touchSimilar to A-3X A-4.5X stretching ratio 1:4.5 Dry to touch Similar toA-3X A-5X stretching ratio 1:5 Dry to touch Similar to A-3X

Example B

A single layer porous polypropylene (PP) film with different stretchratios was prepared as follows: Mix 80% CaCO₃/PP master batch resinpellet (Ampacet 103211 CaCO₃, Ampacet CaCO₃/PP master batch with 70%CaCO₃, density=1.70) and 20% PP resin pallet (Flint Hill HPP,P4G3Z-050F; MFR=4.2, density=0.9). Total proportions in the blend resinwere 56% CaCO₃ and 44% PP. Feed resin pellet blend in extruder A, B, Cand D. The extruder temperature was set as 460° F. Cast roll and MDOrolls temperatures were set as two cast roll T=120° F.; pre-heat 1, 2,3, 4, 5 rolls T=230° F.; stretching 1, 2 rolls T=230° F.; annealing 1and 2 rolls T=230° F.; and cooling roll T=70° F. To make film sampleswith different stretching ratios, the draw ratio between stretching roll1 and stretching roll 2 was set at 1:1, 1:2, 1:3, 1:4, 1:4.8, 1:5respectively for each sample. The banding disappeared after stretching4.8X and above. Corresponding samples collected were labeled as samplesB-1X, B-2X, B-3X, B-3.5x, B-4.8X and A-5X. When the samples werestretched at ratios lower than 1:4, non-uniform banding along CDdirection was observed. The printing results of various samples arelisted below.

Table 2 lists the Eco-Sol inkjet printer printing result of example Bsamples. Compare-4 sample is a mono layer PP film, which has no porousstructure and no absorption capacity so it exhibited very wetcharacteristics. Compare-5 sample is a cavitated biaxial oriented PPfilm available from COSMO. Most pores inside this sample were isolated(not interconnected) and thus could not form continuous channels for inkfluid to flow within the interior of the film. Therefore, this samplewas wet after print. From sample B-1X to A-5X, as the stretching ratioincreased, more interconnected pores were created. When a ratio of 4.8times stretching was reached, the porosity created provided enoughabsorption capability for print, so the print reached a “dry to touch”characteristic.

TABLE 2 Eco-Sol Inkjet Printer Printing Result of Example B andReference Samples Sample ID Sample Description Print Dryness PrintQuality Compare-4 50 micron single layers Very wet, over Nearly no HPPfilm made from 100% 80% ink trans- resolution. Flint hill HPP, P4G3Z-ferred to paper 050F no stretching in MD Compare-5 Cavitated BOPP filmfrom Very wet, over Nearly no Cosmo (60PCT-2 grade) 80% ink trans-resolution. ferred to paper B-1X stretching ratio 1:1 Very wet, Nearlyno approximately resolution. 50% ink trans- ferred to paper B-4.8Xstretching ratio 1:4.8 Dry to touch Similar to A-3X B-5X stretchingratio 1:5 Dry to touch Similar to A-3X

Example C

A single layer porous polyethylene and ethylene vinyl acetate (PE/EVA)blend film with different stretch ratios was prepared as follows. Mix68% CaCO₃/EVA master batch resin pellet (Master batch is compounded byHeritage plastics, 75% CaCO₃ in EVA with 26% binyl acetate,density=1.81, MI=0.32) and 32% HDPE resin pallet (DMDA 8904 NT7 fromDow; MI=4.4 density=0.952). Total proportions in the blend resin were50% CaCO₃ and 32% HDPE and 18% EVA with 26% VA. Feed resin pellet blendin extruder A, B, C and D. The extruder temperature was set as 460° F.Cast roll and MDO rolls temperatures were set as two cast roll T=120°F.; pre-heat 1, 2, 3, 4, 5 rolls T=170° F.; stretching 1, 2 rolls T=170°F.; annealing 1 and 2 rolls T=180° F.; and cooling roll T=70° F. To makefilm samples with different stretching ratios, the draw ratio betweenstretching roll 1 and stretching roll 2 was set at 1:1, 1:2, 1:3, 1:4,1:5, 1:6 respectively for each sample. Corresponding samples collectedwere labeled as samples B-1X, B-2X, B-3X, B-3.5x, B-4.8X and A-5X. Whenthe samples were stretched at ratios lower than 1:4, non-uniform bandingalong CD direction was observed. The banding disappeared afterstretching 5X and above. The printing results of samples are listedbelow in Table 3.

Similar to example B, when the stretching ratio reached 5 times in themachine direction, the samples began to exhibit a “dry to touch”characteristic and exhibit good resolution after print.

TABLE 3 Eco-Sol Inkjet Printer Printing Result of Example C SamplesSample ID Sample Description Print Dryness Print Quality C-1X stretchingratio Very wet, Nearly no 1:1 approximately resolution. 50% ink trans-ferred to paper C-5X stretching ratio Dry to touch Good resolution, 1:5color density is slightly higher than to A-3X, but lighter thanCompare-1 C-6X stretching ratio Dry to touch Same as B-5X 1:6

Example D

A two layer film with a first layer having a microporous structure likeexample C and second layer having no voids was prepared as follows: Feedsame resin blend as in example C in extruder A and B and feed 100% HDPEresin (DMDA 8904 NT7 from Dow). The extruder temperature was set as 460°F. Cast roll and MDO rolls temperatures were set as two cast roll T=120°F.; pre-heat 1, 2, 3, 4, 5 rolls T=170° F.; stretching 1, 2 rolls T=170°F.; annealing 1 and 2 rolls T=180° F.; and cooling roll T=70° F. To makefilm samples with different stretching ratios, the draw ratio betweenstretching roll 1 and stretching roll 2 was set at 1:5. The rpm ratiobetween the extruder A, B and C, D was varied to make film samples withdifferent top layer thicknesses. The top layer thickness was controlledto be 5 microns, 15 microns, 25 microns, and 40 microns. The total filmthickness was 2.5 mil. Table 4 lists the Eco-Sol inkjet printer printingresult of example D. Table 4 indicates that the porous film thicknesshas to be approximately 25 microns to reach “dry to touch” with theRoland Eco-Sol inkjet printer. The minimum thickness may vary slightlybased on the printer design from different manufacturers and heatsettings during printing.

TABLE 4 Eco-Sol Inkjet Printer Printing Result of Example D Sample IDPrint Layer Thickness Print Dryness D-1 Approximately 5 Very wet D-2Approximately 15 wet D-3 Approximately 25 Dry to touch D-4 Approximately40 Dry to touch

Example E-PE

A non-stretched cast film was made using the same process as describedfor Example A. Then the sample was offline stretched by using Karo IVLaboratory Stretcher at a stretch ratio of 3 (CD)X3 (MD). The stretchoven was set at 230° F. with a 60 second heat time, 25% second stretchrate in both CD and MD directions, 5 second annealing in an annealingoven and 0.98 annealing ratio used in both MD and CD.

Example E-PP

A non-stretched cast film was made using the same process as describedfor Example B. Then the sample was offline stretched in MD and CDdirections simultaneously using a Karo IV Laboratory Stretcher at astretch ratio of 3 (CD)X3(MD). The stretch oven was set at 284° F. with60 second heat time, 25% second stretch rate in both CD and MDdirections, 5 second annealing in an annealing oven and 0.98 annealingratio in both MD and CD.

Example F

A microporous film (a single microporous PP film was prepared by biaxialstretching of a beta spherulite polypropylene film. Polypropylene filmwith open cell microporous structure was used. The pore size wasapproximately 50 nm with 41% porosity. The film was formed by biaxialstretching of the beta-nucleated polyprolylene film. Film thickness was25 microns.

Example G

A microporous film (single microporous PP/PE film) was made by biaxialstretching of a beta spherulite PP/PE film. The pore size was in therange of approximately 10 microns to 1 micron.

Example H

This sample was prepared by the laminate process described inassociation with example G. This sample included a film on top of asolid BOPP film with an emulsion based pressure sensitive adhesive.

TABLE 5 Eco-Sol Inkjet Printer Printing Result of Examples E, F, GSample ID Sample Description Print Dryness Print Quality Example E- 3 ×3 stretching in Dry to touch OK quality, but PE-3 × 3 CD × MD less colorsaturation than example F with same printing condition Example E- 3 × 3stretching in Dry to touch Similar to example PP-3 × 3 CD × MD E-PE-3 ×3 Example F A microporous film Dry to touch Good print quality Example GA microporous film Dry to touch Similar to example E-PE-3 × 3 Example HA microporous Dry to touch Print same as film/solid BOPP example GlaminateInk Color Density

Table 6 lists the ink color density of four basic color inks (cyan,magenta, yellow, black) at different loadings. Ink color density of themicroporous samples were slightly higher than Compare-1 sample since thefilm surface is much rougher than high gloss MPI1005SC, giving the sameink loading. There are several different approaches for increasing theink color density on print: (1) slightly increasing the amount of colorink during the printing; (2) smoothing the film surface roughness byusing a gloss embossing or calendar extrusion roll; (3) reducing thesurface pore size via optimizing the extrusion conditions; and (4)adding a thin layer of high gloss porous coating on the surface of thefilm.

TABLE 6 Basic Color (Cyan, Magenta, Yellow, Black) Block Print Ink ColorDensity with Roland Eco-Sol Printer Ink Four Basic Color Block Print InkColor Density Example Loading C M Y K Compare-1 25% 0.53 0.28 0.40 0.5350% 1.03 0.57 0.68 1.15 75% 1.71 1.04 0.85 1.79 100%  2.51 1.89 0.982.39 A-2X 25% 0.35 0.24 0.33 0.41 50% 0.58 0.41 0.51 0.66 75% 0.84 0.780.67 0.93 100%  1.09 1.20 0.75 1.12 A-3X 25% 0.36 0.21 0.33 0.46 50%0.62 0.42 0.52 0.80 75% 0.85 0.67 0.64 0.97 100%  1.02 1.12 0.74 1.13A-3.5X 25% 0.37 0.22 0.34 0.45 50% 0.64 0.44 0.53 0.78 75% 0.88 0.680.66 0.92 100%  1.02 1.11 0.75 1.04 A-4.5X 25% 0.38 0.22 0.32 0.43 50%0.65 0.45 0.50 0.75 75% 0.88 0.69 0.61 0.91 100%  1.01 1.01 0.69 1.07B-4.8X 25% 0.27 0.16 0.25 0.35 50% 0.51 0.37 0.45 0.66 75% 0.82 0.730.61 0.89 100%  1.27 1.43 0.77 1.23 C-5X 25% 0.41 0.24 0.30 0.46 50%0.69 0.53 0.50 0.76 75% 0.88 0.77 0.61 0.81 100%  0.94 1.03 0.65 0.87 G25% 0.34 0.18 0.24 0.33 50% 0.72 0.43 0.49 0.66 75% 1.07 0.81 0.62 1.08100%  1.92 1.70 0.76 1.70 G 25% 0.26 0.16 0.25 0.31 50% 0.48 0.35 0.430.60 75% 0.79 0.69 0.57 0.84 100%  1.18 1.23 0.69 1.06Ink Absorption Result

The ink absorption properties of the samples were evaluated by twomethods: (i) IGT ink penetration test by using IGT Printability testertype A1, and (ii) Nano contact angle and ink spreading test with Eco-Solmax black ink. In the IGT ink penetration test, a drop of ink was passedthrough a nip utilizing a known, controlled pressure. One side of thenip holds a sample of the material being tested. As the ink dropletpasses through the pressurized nip, it spreads out, creating a stain onthe test material. The length of the stain was measured to determine thematerial's holdout properties. In the ink spreading test, a picoliterdrop of ink was ejected from an inkjet nozzle on the sample surface. Ahigh speed optical microscope camera captured unabsorbed ink drop volumeleft on the sample surface as a function of time.

FIG. 4 illustrates the Eco-Sol max black ink absorption of microporoussamples and non-porous samples. Samples A-4.5X, B-4.8X, F and G had muchhigher absorption speed than Compare-1 sample (MPI1000SC). This enablesthe noted samples to be printed at higher speed. This in turn increasesprinting efficiency. FIG. 4 also shows ink absorption speed of examplestested by the Nano contact angle instrument.

Table 7 lists the IGT ink penetration length of the samples and porosityof film based on density calculation. Samples with IGT ink penetrationlength equal or greater than 16 cm and porosity less than 40% were stillwet after print.

TABLE 7 IGT Ink Prenetration Length of Different Samples Sample ID IGTInk penetration Length (cm) Porosity A-1X 18.20 Approximately 10% A-3.5X10.70 Approximately 40% A-4.5X 10.10 Approximately 40% B-4.8X 12.03Approximately 44% C-5X Approximately 40% F 10.6 Approximately 55% G 14.8Approximately 40% H 16.6 Approximately 30%

Table 8 lists the water based inkjet printing results of selectedsamples printed with an Epson WF-3520 desktop water based inkjetprinter. The results demonstrate that the open cell microporous sampleshave enough water absorption management capability to reach “dry totouch” after print. Application of a very thin layer even less than 1micron thick, of a porous inkjet printable top coating on top of thistype of microporous film may further improve the ink anchorage andenhance surface smoothness based on application need.

TABLE 8 Water Based Inkjet Printing Results of Selected Samples SampleID Print Dryness Print Quality C-1X Very wet Significant bleeding C-5XDry to touch Ok image resolution, slightly reduced color density C-6XDry to touch OK image resolution, slightly reduced color density F Dryto touch Good image resolution G Slightly wet at high See some bleedingwith high black ink loading color loading black ink.

Many other benefits will no doubt become apparent from futureapplication and development of this technology.

All patents, applications, standards, and articles noted herein arehereby incorporated by reference in their entirety.

The present subject matter includes all operable combinations offeatures and aspects described herein. Thus, for example if one featureis described in association with an embodiment and another feature isdescribed in association with another embodiment, it will be understoodthat the present subject matter includes embodiments having acombination of these features.

As described hereinabove, the present subject matter solves manyproblems associated with previous strategies, systems and/or devices.However, it will be appreciated that various changes in the details,materials and arrangements of components, which have been hereindescribed and illustrated in order to explain the nature of the presentsubject matter, may be made by those skilled in the art withoutdeparting from the principle and scope of the claimed subject matter, asexpressed in the appended claims.

What is claimed is:
 1. A method of forming a polymer film adapted forabsorbing liquid inks from inkjet printing, the film defines a firstface for receiving print and a second oppositely directed face, the filmincluding a microporous structure extending along at least one face ofthe film, the method comprising: extruding polymer to form a film;stretching the film to a stretch ratio within a range of from 1:1.1 to1:10 such that the microporous structure has a porosity within a rangeof from 40% to 75% and includes a plurality of interconnected poreshaving a pore size distribution within a range of from 2 microns to 10nm, wherein the film exhibits an ink absorption rate of at least 0.01picoliter/μm²/second at a printing temperature of 40° C.
 2. The methodof claim 1 wherein stretching the film is performed inline.
 3. Themethod of claim 1 wherein stretching the film is performed off line. 4.The method of claim 1 wherein stretching the film is performed in asingle direction.
 5. The method of claim 1 wherein stretching the filmis performed in both a machine direction and a cross direction.
 6. Themethod of claim 1 wherein stretching is performed such that the stretchratio is within a range of from 1:2 to 1:8.
 7. The method of claim 1wherein the film after stretching includes the microporous structurehaving a thickness of at least 20 microns.
 8. The method of claim 1wherein the film includes at least one polyolefin.
 9. The method ofclaim 8 wherein the film includes at least 30% polyolefins.
 10. Themethod of claim 9 wherein the film includes at least 40% polyolefins.11. The method of claim 10 wherein the film includes at least 50%polyolefins.
 12. The method of claim 8 wherein the polyolefin isselected from the group consisting of polyethylene, polypropylene,polyethylene copolymer, polypropylene copolymer, and combinationsthereof.
 13. The method of claim 1 wherein the porosity is within arange from 40% to 70%.
 14. The method of claim 13 wherein the porosityis within a range of from 40% to 60%.
 15. The method of claim 1 whereinthe film includes at least one inorganic filler.
 16. The method of claim15 wherein the at least one inorganic filler is present within a rangeof from 30% to 70% by weight.
 17. The method of claim 1 wherein the filmcomprises at least one polyolefin and at least one polymer incompatiblewith the at least one polyolefin, the at least one polymer selected fromthe group consisting of polystyrene, styrene copolymer, polyurethane,polyester, polyacryl resin, polymethacryl resin, polycarbonate,ionomers, and combinations thereof.
 18. The method of claim 1 whereinthe film comprises a beta polypropylene crystal phase.
 19. The method ofclaim 1 wherein the film is stretched in only a machine direction (MD).20. The method of claim 1 further includes the step of applying a topcoat on the first face, wherein the top coat includes a microporousstructure to thereby improve ink anchorage and/or surface smoothness.21. A method of forming a polymer film adapted for absorbing liquid inksfrom inkjet printing, the film defines a first face for receiving printand a second oppositely directed face, the film including a microporousstructure extending along at least one face of the film, the methodcomprising: extruding polymer to form a film; stretching the film to astretch ratio within a range of from 1:1.1 to 1:10 such that themicroporous structure has a porosity within a range of from 40% to 75%and includes a plurality of interconnected pores having a pore sizedistribution within a range of from 2 microns to 10 nm, wherein the filmcomprises of at least one beta polypropylene crystal phase and at leastone inorganic filler.